This invention relates to a system for monitoring conditions within a tire, and specifically to a receiver assembly for receiving transmissions of varying modulations from sensor assemblies within each of the tires and from a remote keyless entry system. It is becoming increasingly desirable to continually monitor tire pressures in a motor vehicle during operation. Such constant monitoring of tire pressures allows an operator to maintain vehicle tire pressures within an optimal range to optimize fuel economy and handling performance.
Conventional methods of monitoring tire pressure include positioning a sensor within each wheel to monitor pressure. The sensor assembly typically emits a radio frequency (RF) transmission indicative of tire conditions. A receiver disposed within the vehicle receives the RF signal and actuates a messages or warning light to signal the operator of tire conditions.
Many motor vehicles include a remote keyless entry system including a key fob carried by an operator to actuate door locks or other features. The remote keyless entry system includes a receiver disposed within the motor vehicle to receive transmissions from the key fob and actuate vehicle systems in response to transmissions received from the key fob. It is known in some system to utilize the same type of transmission for the tire monitoring system as is used in remote keyless entry system.
Typically, a transmission is modulated either as an amplitude shift keyed ASK, or a frequency shift keyed FSK radio frequency. The ASK transmission modulation is best suited for applications in which the receiver and transmitter are relative stationary to each other. In addition ASK transmissions are favorable when there exists a relatively long distance between the transmitter and the receiver. However, an ASK transmission becomes disrupted when the receiver or transmitter is moving relative to one another. The FSK signal is suited for transmitters that are moving relative to the receiver because the amplitude remains essentially constant for the duration of any transmission. However, the FSK transmission has lower peak field strength than a comparable ASK transmission. The FSK transmission is specifically suited for use with the sensor assembly disposed within the tire and the ASK is suited for use with the remote keyless entry system.
Accordingly, it is desirable to develop a receiver capable of receiving both ASK and FSK transmissions to optimize the capabilities of both the tire monitoring system and the remote keyless entry system.